replace prep_libc.sh with prep_libc.py, and quiet the output

base/allocator/allocator.gyp

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     'jemalloc_dir': '../../third_party/jemalloc/chromium',
     'tcmalloc_dir': '../../third_party/tcmalloc/chromium',
   },
   'targets': [
@@ skipping 435 matching lines @@
   'conditions': [
     ['OS=="win"', {
       'targets': [
         {
           'target_name': 'libcmt',
           'type': 'none',
           'actions': [
             {
               'action_name': 'libcmt',
               'inputs': [
-                'prep_libc.sh',
+                'prep_libc.py',
               ],
               'outputs': [
                 '<(SHARED_INTERMEDIATE_DIR)/allocator/libcmt.lib',
               ],
               'action': [
-                './prep_libc.sh',
+                'python',
+                'prep_libc.py',
                 '$(VCInstallDir)lib',
                 '<(SHARED_INTERMEDIATE_DIR)/allocator',
               ],
+              'msvs_cygwin_shell': '0',
             },
           ],
         },
         {
           'target_name': 'allocator_unittests',
           'type': 'executable',
           'dependencies': [
             'allocator',
             'allocator_extension_thunks',
             '../../testing/gtest.gyp:gtest',
@@ skipping 24 matching lines @@
           'configurations': {
             'Common_Base': {
               'msvs_target_platform': 'x64',
             },
           },
         },
       ],
     }],
   ],
 }